1. Field of the Invention
The present invention relates to a method of adjusting a reception threshold value in data reception, and more particularly to a method of adjusting the reception threshold value of a reception signal to minimize the influence of a crosstalk signal from a transmission part on a reception part of a data transmission and reception module, and a data transmission and reception module using the method.
2. Description of the Related Art
Along with the demand for a wider bandwidth of a data network, the need for an increase of the capacity and the speed in data transmission has been increasing. For example, an optical communication device providing a transmission bandwidth of 10 Gbit/s has been increasingly introduced. A 10 Gbit/s optical transceiver module, which is a data transmission and reception module implementing the optical communication device, has been spreading, promoted by an industry standard called MSA (Multi Source Agreement). As a result, the improvement in performance and the reduction in size and cost of the module have been in progress. For example, in an XFP (10 Gbps Small Form Factor Pluggable) module compliant with the MSA, a transmission part and a reception part are integrated together to reduce the size of the module. As compared with a conventional 300-pin MSA SFF (Small Form Factor) optical transceiver module, the XFP module needs to be reduced to one sixth in size and one third in power consumption. The specification of the XFP module is disclosed in XFP REVISION 4.5 SPECIFICATION (<http://www.xfpmsa.org/cgi-bin/msa.cgi>).
In the reduction in size of a module, it is necessary to reduce the sizes of the transmission part and the reception part while improving the characteristic of the module. Particularly, in a module in which the transmission part and the reception part are integrated together, as in the XFP module, a crosstalk from the transmission part to the reception part constitutes a serious problem for the improvement in performance of the reception part. Techniques of removing a crosstalk signal include, for example, a technique described in Japanese Unexamined Patent Application Publication No. 2005-130303.
To improve the characteristic of the transmission part of the data transmission and reception module, the amplitude needs to be increased. Meanwhile, to improve the reception characteristic, a high-sensitivity APD (Avalanche Photodiode) device or the like is used, and thus the signal amplitude is substantially reduced. Therefore, to improve the reception characteristic of the data transmission and reception module in which the transmission part and the reception part are integrated together, as in the XFP pluggable module, for example, it is important to remove the crosstalk from the transmission part as much as possible. In such a module, however, the transmission part and the reception part are close to each other due to the small size of the module. Therefore, it is difficult to completely remove the crosstalk from the transmission part to the reception part.